Blender 2.8 and Caustics in YafaRay and POV
LuxCoreRender is able to use bidirectional path tracing with CPU rendering that is more suitable to render caustics. It is also free and open source and its integration to Blender is alright. It is worth having a look. 



It takes a long time, but it works. You need to select Bidir engine and Metropolis sampling seems to work best: